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In this paper, the concept of network security and security structures of OSI and Internet is introduced, and various threats confronting the computer network are also discussed. Several kinds of network information security technologies, including firewall technology, virtual private network, intrusion detection system, data encryption technology, identity authentication and security protocol etc. are also examined. The security of internal network is the biggest problem in the construction of each network. The solution to this problem lies in setting up a firewall. The theory of a firewall and the approach to its actualization is studied. Intrusion detection system, an important part of the computer network security system, has gained extensive attention. IDS monitors the computer and network traffic for intrusion and suspicious activities. It not only detects the intrusion from the extranet hacker, but also the intranet users. The emergence of virtual private network paves the way for realizing secure connection of LAN quickly and at a relatively low cost. The concept, function, key techniques, including the tunnel technology, and the ways to realize VPN are expounded in this paper. Also introduced is the data encrypt network technology, which is called the soul of computer network security, such as digital digest, digital signature, digital certificate, digital encrypt arithmetic and so on. At the same time, the principle and the process of implementing network security by digital certificate and digital signature, the basic principle and characters of security protocols, and finally, three of the security protocols, concerning the security problems in network, IPsec, SLL and SET are analyzed in detail Computer network system should be a system of dynamic defence, both dynamic and static, passive as well as active, and even offensive, combined with management and technology.

本文系统地介绍了网络安全的概念、OSI及Internet的安全体系结构，并讨论了计算机网络面临的各种安全威胁；内部网络的安全问题是每个建网单位面临的最大问题，可以认为防火墙技术是解决网络安全的一个主要手段，本文研究了防火墙的原理及其实现手段；作为一种主动的防御措施，入侵检测系统作为网络系统安全的重要组成部分，得到了广泛的重视，TDS对计算机和网络资源上的恶意使用行为进行识别和响应，不仅检测来自外部的入侵行为，也监督内部用户的未授权活动；虚拟专用网技术的出现，为实现网络间的连接提供了快速安全但又相对便宜的手段，本文较深入的探讨了实现VPN的隧道技术，并对VPN的概念、功能、实现途径、基本构成、关键技术及发展前景等问题进行了全面论述；数据加密技术是网络安全核心技术之一，本文从数据加密算法、数字摘要、数字签名及数字证书等几方面简要介绍了数据加密技术，并分析用数字证书和数字签名实现网络安全的原理和过程；对安全协议的基本原理、主要特点进行了较为深入的研究，并就网络的安全性问题剖析了三种安全协议：IPsec协议、SLL协议和SET协议。

By finding a set of basis, we use matrices of transformation under a set of basis to describe the structure of the Galois group. If a normal extension has a normal basis, then it is simpler to describe the structure of Galois group in this method.

因此寻找一组基，我们利用线性变换在基下的矩阵来描述Galois群的结构，特别地，当正规扩张存在一组正规基时，用这种方式表示Galois群的更加简单。

Finding the most cost-effective way to ship goods between a set of factories and a set of stores defines a network flow problem, as do resource-allocation problems in communications networks and a variety of scheduling problems.

找到最符合成本效益的方式之间运送货物的一系列工厂和商店的一套定义了网络流问题，因为这样做资源分配问题的通信网络和各种调度问题。

Particularly,when A is positive,we give a detailed characterization of the set ∏={Q∈∏:R=S⊥,AQ=QA},where ∏ and S⊥ denote the set of all idempotents on H and the orthogonal complement of S,respectively.

特别地，当A是正算子时得出了集合∏={Q∈∏：R=S⊥，AQ=Q*A}非空的充要条件；并且对集合∏进行了详细的刻化，这里∏和S⊥分别表示一个复Hilbert空间上的所有幂等算子构成的集合和子空间S的正交补空间。

This is a language where 'cleave' can mean to cut in half or to hold two halves together; where the simple word 'set' has 126 different meanings as a verb, 58 as a noun, and 10 as a participial adjective; where if you can run fast you are moving swiftly, but if you are stuck fast you are not moving at all; where 'colonel,' 'freight,' 'once,' and 'ache' are strikingly at odds with their spellings.

在英语里，"劈"既可以是指一切为二的意思，又有把两样东西粘合在一起的意思；一个简简单单的"SET"，作动词时，就有126种不同的意思，而作名词用时，又有58个意思，作为分词形容词是，则又有10种意思了；英语里，如果说你跑地快，说明你移动的迅速，但是快这个次在与粘用在一起时，这时的快就不是原来那个意思了；名词colonel、 freight和once则与它们的拼写形成鲜明的对比。

Firstly, this paper definited pseudometric d for n -foldproduct of σ-algebra A of subsets of a given set X , and definited indicator function ; secondly, gave the concept of differentiable of set function at S° and concept of partial derivative at S° with respect to the ith argument Si through indicator function, and defound the weak efficient solution of and optimality necessary condition; Finally, obtained three weak duality results and strong duality results under generalized convexity conditions.

首先，对已知集X的子集的σ-代数A的n-折积A^n，定义了伪度量d，给出了相应的特征函数〈h，Is〉；其次，通过特征函数给出了集函数在S 可微的定义及集函数在S 关于第i个变量Si的偏导数定义；给出了多目标规划问题的弱有效解概念及的最优性必要条件；最后，分别在目标函数和约束函数的3种较弱凸性条件下，研究n-集函数多目标规划问题的对偶问题，获得了3个弱对偶结果和强对偶结果。

Is a wholly-owned enterprises, with strong technical force, a set of quality assurance system, the detection means complete, of well-equipped, with a strong production capacity and can withstand the rubber plant, a complete set of tire plant equipment.

属独资企业，具有雄厚的技术力量，有一整套质量保证体系，检测手段齐全，工艺装备精良，具备强大的生产能力，并能承受橡胶厂、轮胎厂的全套设备。

Miss Bai Lingli have had two sets of super-million dollar downtown housing, a set of self-occupied, a set of investment, but now she also asked a friend to find new housing, and she had not been around a lot of friends in real estate investment affected, have considered the approach to invest because they believe that the property market will continue to rise.

百丽小姐有两套超百万美元的市区住房，一套自住，一套投资，但现在她还问朋友寻找新的住房，和她没有很多周围的朋友房地产投资的影响，已考虑投资的做法，因为他们认为，房地产市场将继续增加。

According to China Everbright Bank branch in Jinan fiscal manager, said the sun set on the 5th asset management plan is "Everbright Sunshine" series of products together another silver certificate, a new work, flexible style of sound, steady income for the highest in the A-share market the prospect of not clear, the sun set on the 5th asset management plans to hedge the value of individual investors is a good choice for family financial planning, rational distribution of the assets of the ideal investment tool.

据中国光大银行济南分行理财经理表示，阳光五号集合资产管理计划是"光大阳光"系列产品银证联手的又一款全新力作，风格稳健灵活，收益稳中求高，在A股市场前景暂不明朗的情况下，阳光五号集合资产管理计划将是个人投资者避险增值的上佳选择，也是家庭理财规划、合理配置资产的理想投资工具。

A 3rd-Runge-Kutta-5th-WENO scheme is used in this study to get solution of the Level Set advection equation. A Projection method is used to solve the N-S equation, and different discretization schemes are presented. A TDMA algorithm is used to solve the energy equation. With the use of these methods, a numerical simulation of vapor-liquid two-phase flows during condensation with large density ratio has been successfully realized.

本文应用三阶Runge-Kutta－五阶WENO组合格式求解Level Set输运方程，应用投影法求解气－液两相流流场N-S方程，给出了不同投影法的具体格式，应用TDMA算法求解气－液两相流场的能量方程，成功实现了对大密度比气－液两相流冷凝流动问题的数值模拟。

By the time of its fall, most of the prisoners were writers who had written against the corruptions of the government.

到它被攻陷的时候，里面多数的犯人是写了反对政府贪污文章的作家。

The most obvious variation to ovum morphological character was that the color was changed from light green to sepiaceous in embryonic development, and all the ovums were almost hatched after 96h.

在胚胎发育过程中卵的形态特征最明显的变化是颜色从淡绿到深褐色，卵在发育96h后卵基本全部孵化。